How to add a shortcut for 'Reload Scripts'?
New shortcuts can be added in the preferences Edit > Preferences > Keymap. 

With the keymap tab open, navigate to the Window category of shortcuts. Click the Add New button to create a new shortcut. The operator for reloading scripts is bpy.ops.script.reload() therefore the identifier for the shortcut is script.reload. Click on the shortcut field and press F8 to set the key binding.



In the default keymap for Blender 2.80 there is no existing key binding on F8 which means you can add the shortcut without any problem.